Just suppose I asked a dumb question like, "Which is better, the 7x57 Mauser, .284 Win. or .275 Rigby?" In that question I would have cited three common conventions in naming cartridges: European, American and British. The European method is most precise because it's almost always given as the bullet diameter in millimeters followed by the case length in millimeters. As in "7x57" means a 7mm (.284-inch) bullet with a 57mm (2.235-inch) case.
American cartridges most commonly use the bullet diameter, followed by a word or words denoting the unique case dimension. ".284 Win." means .284-inch (7mm) bullet diameter, cartridge standardized by Winchester. However, we Americans are inconsistent because we often round the bullet diameter up or down. For instance, a .280 Rem. uses a .284-inch bullet. In general we shy away from metric designations, but we do have American cartridges with metric designations, such as 7mm Rem. Mag.
The British have been least consistent of all. They almost never use metrics, but, as we do, they often use actual bullet diameters (.375 H&H with .375-inch bullet), and round down and occasionally up just as we do. More confusing, however, is they sometimes use the barrel's smaller land diameter rather than the groove or bullet diameter. The .318 Westley Richards, for instance, is actually a .33 caliber cartridge using a .330-inch bullet. Similarly, the .275 Rigby is simply a British designation for the 7x57 Mauser, with identical case dimensions.
Shortly after World War II, Great Britain started divesting herself of far-flung colonies, and her once-robust gun trade withered, so relatively few of the many British sporting cartridges are readily available today. There are exceptions, such as the .375 H&H and .416 Rigby, but the vast majority of today's cartridges are either American or European in origin.
Starting with the 6.5mm and working up, there are often parallel choices between European metric cartridges and American "English" cartridges. Many metric cartridges are virtually unknown over here, but here's how I see some of the popular choices stacking up.
Let's start with the "mild" 6.5mms. In the 1890s, when smokeless powder velocities were new, several similar 6.5mm military cartridges were adopted by European powers and also Japan (the 6.5x50 Arisaka). Civilian 6.5mm cartridges followed. Several were once popular, but the 6.5x55 Swedish Mauser, introduced in 1894, still has an international following. I've seen it used on moose in Sweden and on pigs in California, but I have never owned a 6.5x55 — although it's on my bucket list.
Older cartridges such as this were designed for use with long, heavy-for-caliber bullets. This means that they are too long to chamber into a short (.308 Win.-length) action, but with the shorter, lighter bullets we tend to use today, action space is wasted in a .30-06-length action.
The other problem with rounds such as the 6.5x55 is that most factory loads are mild out of concern for use in older rifles. Norma has a 139-grain 6.5x55 factory load at 2,690 fps, closer to what the cartridge iscapable of, but most American factory loads are downloaded to 2,550 fps. So today the 6.5x55 is primarily a handloader's cartridge. Modern counterparts include the .260 Rem., 6.5-284 Norma and Hornady's 6.5 Creedmoor. All three fit into short bolt actions, and all three are loaded to the gills. Technically, the 6.5x55 has more case capacity for handloaders than the .260 Rem. and is faster, but with their short, fat cases the 6.5-284 and the Creedmoor are both faster still. The 6.5-284 actually comes close to .264 Win. Mag. velocity.
With low recoil and the excellent velocity retention of aerodynamic 6.5mm bullets, all three modern "mild 6.5s" are used in both NRA highpower and 1,000- yard competitions. As for hunting, all of these mild 6.5mms are excellent deer/ antelope cartridges and with the right bullets can serve as minimalist choices for game up to elk — as tens of thousands of Swedish moose hunters know.
I don't have enough experience to suggest the 6.5x55 cannot be as accurate as the three modern choices, but it is generally not considered a tack-driving cartridge. I've had four different .260 Rem. rifles, and although adequate for hunting, none of the four were consistently or exceptionally accurate. I claim little experience with the 6.5-284, a popular wildcat standardized by Norma in 1999. I have taken the 6.5 Creedmoor out to 1,000 yards, and it's amazing what this little cartridge will do.
If you handload, like a whiff of nostalgia and aren't bothered by a longer bolt throw, the 6.5x55 is probably for you. But if you see an advantage to a shorter, lighter and more rigid short action and want maximum performance from a light-recoiling 6.5mm, I'd bypass the .260 and go straight to the 6.5-284 Norma or the 6.5 Creedmoor.
Let's move up to the heavy hitters in the 6.5 category. The 6.5x68, introduced by Germany's RWS in 1939, remains more popular in Europe than the .264 Win. Mag. is over here. Introduced in 1958, the .264 took off like a rocket but began to fizzle when Remington brought out the unquestionably more versatile 7mm Rem. Mag. in 1962. The .264 never really recovered, and today it's sort of just hanging on.
The two are similar in performance. The 6.5x68 is rated at 2,920 fps with a 140-grain bullet, and the .264 is rated at 3,030 fps. Both are generally handloaders' cartridges today, although Nosler alone offers a significant array of .264 factory loads.
With good handloads the two are almost identical, and both are wonderfully flat-shooting cartridges for mountains and plains. Because brass and loading data are scarce for the 6.5x68, I'd have to give the nod to the .264 — a cartridge I've had a soft spot for since I was a kid. Alas, it needs a 26-inch barrel to achieve its potential.
However, if I were looking for a fast 6.5mm right now, I'd probably bypass both and go straight to either the .26 Nosler or the brand-new 6.5-.300 Wby. Mag. The Weatherby has an edge in velocity, while the Nosler has a more modern unbelted case. Right out of the box both are 200 fps faster than the best loads I can gin up for my .264 Win. Mag., and today we have plenty of good bullets that hold up at such high velocity.
On to the mild 7mms. This is a tough one for me because I love the grand old 7x57 Mauser (or, if you prefer its British moniker, the .275 Rigby). It has essentially the same problems as the 6.5x55. It cannot be housed in a true short bolt action, and most factory loads are conservative because of possible use in older rifles. Current loads show a 140-grain bullet at 2,660 fps? Really?
Anyway, the 7mm-08 cures both problems. Based on the .308 case, it fits into short actions, and the standard factory load is a 140-grain bullet at an impressive 2,860 fps. The 7x57 has greater case capacity and can exceed this with careful handloading for modern rifles, but if you shoot factory loads the 7mm-08 wins.
I've had a string of 7x57s over the years, but I outfitted both my daughters with 7mm-08 rifles because of the shorter, lighter actions and greater selection of factory loads. My experience has been that with its shorter and more efficient case the 7mm-08 is the more accurate of the two, with more modern load development probably contributing. That said, both are plenty accurate for the medium-range hunting they are suited to, and both are fully adequate for game up to elk.
My choice remains the 7x57, but when asked about efficient, mild-recoiling hunting cartridges, I tend to recommend the 7mm-08.
There are two contestants in the midrange power 7mm category: 7x64 and .280 Rem. The 7x64 Brenneke was introduced by Wilhelm Brenneke in 1917. It is almost identical to the .280 Rem., introduced 30 years later, but they are not interchangeable due to tiny differences in rim and base diameter and the .280 case is .020 inch longer. Both, however, are nominally .30-06-length. The biggest difference is the older 7x64 has more body taper and therefore doesn't equal the case capacity of the .280.
This makes the .280 theoretically the faster cartridge. However, European factory loads are often a bit hotter than American loads, so published velocities between the two are fairly close. Also, the 7x64 is popular enough in Europe that there are American loadings for it.
There isn't much to pick between the two cartridges because they are identical in performance. Although a superb hunting cartridge, the .280 Rem. has never been wildly popular, but here in the United States it is certainly much more available than the 7x64. So if you see a good deal on a 7x64 don't walk away from it, but in this country, based only on availability, the nod must go to the .280.
There's a host of 7mm magnums today, but they're all of American origin, so let's step up to the 8mm and pit the 8x68S against the 8mm Rem. Mag. The 8mm bullet diameter standardized in 1904 as the 8mmS with .323-inch bullet has never been popular in North America. I remain a staunch fan of the 8mm Rem. Mag. as an ideal elk cartridge, but I'm one of its few supporters. The 8x68S was introduced in 1939, a companion to the 6.5x68 that uses the same parent case.
The 8mm Rem. Mag. has considerably more case capacity and thus is theoretically faster. But once again you get into differences between conservative American factory loads versus their European counterparts, so with factory loads the two are almost identical, and both should be considered similar in hunting performance to the .338 Win. Mag.
Although it's definitely pushing the limit, the 8x68S will fit into a .30-06-length action, while the 8mm Rem. Mag. is based on the .375 H&H case and needs a full-length action. Due to limited popularity, 8mm Rem. Mag. factory loads are scarce, but the 8x68S is almost unheard of here.
Maybe few people care about the 8mms, but they certainly care about the differences between the 9.3mm and .375 H&H. The 9.3mm, bullet diameter .366, is essentially the European equivalent of the .375. We often say the African "legal minimum" for dangerous game is .375, but that's British and American arrogance because the actual minimum is more often 9.3mm.
In terms of bullet diameter the .375 and 9.3mm are too close to argue about, and the 9.3mm has long been supplied with heavy-for-caliber bullets up to 293 grains. So the comparison comes down to case dimensions and velocity.
The unbelted 9.3x62 Mauser is easily the most popular, fits handily into a .30-06-length action and has made a bit of a comeback in the United States, with modern factory loads available from Hornady and Norma. With a 286-grain bullet at 2,360 fps, it is not the equal of the .375 H&H, but it's a mild-recoiling load that should be considered a bare-bones minimum standard for African buffalo.
Ballistically identical, and probably second most popular, is the rimmed 9.3x74R designed for use in single-shots and double rifles. It is also loaded in both the United States and Europe. Like the 9.3x62, I'd consider it a bare-bones choice for buffalo, but I'd be nervous about its use on elephant.
Better than either is the 9.3x66, introduced by Federal in the United States in 2009 as the .370 Sako Mag. It is based on the .30-06 case, but with a slightly longer case and short neck, it has more case capacity than the 9.3x62, and, as a new cartridge intended for modern rifles, it is loaded to the gills.
Federal's 286-grain bullet is rated at 2,550 fps. This may be a bit optimistic, but even so the cartridge comes very close to the .375 H&H in performance. Able to be housed in a .30-06-length action and with compact ammo, it should be catching on better than it has, but so far it has not been popular.
Regrettably, much the same must be said about the 9.3x64 Brenneke, a 1927 Wilhelm Brenneke cartridge that was very much ahead of its time. Using a short, fat (.504-inch rim, .492-inch base), unbelted case, the 9.3x64 can be housed in a .30-06-length action (with bolt face opened). It is clearly a forerunner of our modern unbelted magnums. With a 293-grain bullet at 2,580 fps, it actually exceeds standard velocities for the .375 H&H and must be considered at least its equal, but it's almost unknown in the U.S. and there are no American factory loads.
All said, I'm really more of a .375 guy, but my old friend the late Chub Eastman became a 9.3mm fan in his later years and tried them all. There are no significant ballistic advantages, but the 9.3mm cartridges definitely offer viable alternatives to the .375.